Early Renold’s Chain Drives, 1917
In this article are scanned pages from a 1917 leaflet from Renold Chain, sent to us by reader Nick N. The time of the publication was an interesting era, as the belt drives that were so common in the UK had been recently challenged by chain drive. (Chains had been adopted in the USA much earlier, but only a few Brit makers embraced them.) While belts were preferred by UK riders due to their simplicity and smoothness, recent advances in 1914 and 1915 had brought countershaft gearboxes into cycles. Thus the primary chain drive was also required, with a simple sprocket on the motor mainshaft, and another on the gearbox mainshaft or clutch hub. At this time, and up through the mid 1920’s it was common to have a chain primary drive, with a belt drive from the gearbox to the rear wheel. This was termed a chain-cum-belt.
Premier Chain-cum-belt drive
This layout had the advantages of both drive systems (but the cynic will note that it also had the disadvantages of both!). Namely the belt gave a smooth drive to minimize the shocks from the one or two cylinder motors working on the Otto cycle. And the chain didn’t slip when wet, and could bend around small diameters to give some flexibility to the designer as he set the gearing and the resultant torques and component speeds. Small pulley diameters were an issue for belts, as they couldn’t readily bend around little motor pulleys. And the rear wheel pulley could not be any larger than the wheel rim diameter, so the lowest gearing possible with belt drive was set by this geometry. With a chain primary drive including a small gear reduction, the belt final drive had less of a gear reduction ratio and could afford a larger front pulley to reduce slippage. Of course, the countershaft gearbox and chain drive did much more. By providing a simple, robust location to put the clutch, footstarter, and 2 or 3 gears, it revolutionized how motorcycles were ridden. Looking at a modern 220hp superbike, you’ll see a countershaft gearbox right behind the crankshaft, with chain drive or maybe gear drive between the two. It may have 6 or 7 gears and a foot shifter, but the concept is still recognizable as being derived from those used in 1914.
Renold was clever to show the Sunbeam in the literature, as Sunbeam went with chain drive from their very first motorcycle built in Sunbeamland. The Veteran ‘beams were very advanced bikes, and John Marston and team were designing their bikes to a high standard, not down to a low cost. Sunbeams ran their chains inside sheetmetal covers called the “little oil bath” with lubrication to increase the chain life. This feature was also used on their pedal cycles. Another feature was the engine shock absorber (ESA) which was a spring coupled device on the mainshaft that took up some of the shock of the motor’s power pulses. Without such a device, chains transmitted too much vibration to the rider, as well as fatiguing the bike parts toward failure. All makes of bikes gained a cush drive of some sort eventually, but the early designs lacked an ESA.
The last few pages of the brochure involve chain driven generators/dynamos. These were just becoming popular in the era, and Renold was hoping to grow the business with the promise of numerous nighttime riders. The last pages even list what time of day to turn on lights, and the hour of sunset for various locations and months. Ultimately, belts were more commonly used to drive generators, but chain driven magnetos were used extensively for decades after WWI. The reason being that a little belt slip didn’t affect generators, but it would drastically change the ignition timing.
As usual, click on the image to see a large version. They are nice big scans and should be easy to read when you zoom in.